Audio or Vibration sensing

[Jack.Straw]

Hello. I've built a cigar box guitar with tiny LED's installed under the fretboard inlays. Does anyone know here know of a device that i could put between the power supply (2 AA) and the lights that would make them turn on when the guitar is played? It could be a sound sensing circuit or a vibration sensing device. A device that would make the lights flash like an equalizer would be very cool too! I'm looking for a very low cost solution.

Thanks for any advice you can offer!
-Jack

 

[rikie_rizza]

Use a microphone (as sensor) -> amplified -> band pass the frequency (usually bass) -> digitize (maybe you dont have to) -> LED

 

[Jack.Straw]

I ended up purchasing a "color organ" kit, which does basically what you said. I ordered this one:

**broken link removed**

During assembly I intend to bypass the 4 LEDs on the board and connect my LED strand instead. Think that will work? There are 10 rice LEDS in-line on the strand, but I could trim off a couple if I had to..

Thanks for the advice,
-Jack

 

[rikie_rizza]

It should work...go ahead try, inform me the result.

 

[Jack.Straw]

I've assembled the color organ, but i haven't moved forward because i'm concerned about voltage. The string of LEDs in the guitar originally ran on 2 AA batteries (2x 1.5v = 3v). The color organ with 4 LEDS runs on a 9v battery. I don't want both batteries in the guitar, and i'd like the option of bypassing the color organ, so I'm going to use a 2 circuit switch like this:

What would I use to reduce the voltage when the switch is in position 1? Do you think i need to? I guess i may also need to see how many volts the board LED ports are pushing too. I don't have a low voltage tester yet though..

 

[rikie_rizza]

Can you just skip the bypassing? I'm afraid that the voltage feed can be reversed...you know, the voltage from the batt get in the color organ circuit from the led. You don't know that the color organ circuit has a voltage regulator or not...if it does, feed with 9 volt will burn your circuit.
Without bypassing, just use 9V...with bypass, use diode 1N4001 to make sure that the voltage cannot enter the circuit.

To lower the voltage...use voltage divider or voltage regulator 7805, don't forget to reduce the current using 100ohm in series with the led.

 

[Jack.Straw]

Rikie,

Thanks for your help! I've spent the last couple hours reading and my head is spinning. I found plenty of voltage divider calculators, but i'm still confused as to what resisters to use. Below is my re-design using your advice:

Is that close? Using the online voltage divider calculators I can see that when reducing 9 volts to 3 volts the relation between R1 and R2 is always 50%, but I have no idea what ohm to use.

Thanks again for all your help!
-Jack